Removing Alpha Channel in Node Editor
To help troubleshooting, add an emission node and set it as alpha channel viewer, because it looks like there is an uncorrect alpha channel.

An useful shortcut for this procedure is to enable the Node Wrangler Add-on and Shift Ctrl click on a node a couple of times to temporarily view its output values.



Also checking the image in a 2D app (Gimp, Photoshop) could help, because the Blender setup looks correct.